Researchers at The Jackson Laboratory have a long and successful track record in training a cadre of research scientists in the complexity of regulation of gene expression and the role of intercellular signaling in developmental decisions in mice. This philosophy, an integral part of the Laboratory's strategic plan, has dictated the ongoing expansion of the overall training program at The Jackson Laboratory, which requests funding for continuation of its well-established postdoctoral research training program in developmental genetics. Fourteen members of The Jackson Laboratory Research Staff form an interdisciplinary pool of trainee preceptors who are investigating pre-implantation and post-implantation embryonic development, germ cell differentiation, eye development, primary sex determination, and the developmental regulation of homeostatic mechanisms in adult animals. These types of analyses are made possible by the availability of the Laboratory's unparalleled resource base of special inbred, spontaneous and induced-mutant mice, and curated knowledge about them. Support is requested for four trainees, who will devote their major effort to bench research, and are integrated into The Laboratory's seminars, courses, workshops, and research interest groups. They are required to write fellowship applications, and present their results both at in-house interest groups and international meetings. Their progress is overseen by a formal Training Committee, in which each member acts as an informal mentor, or liaison, for several trainees. Upon completion of training, participants will be qualified to engage in creative, independent research in developmental genetics at a university, research institution, or in industry. The continued quality of the program is evidenced in part by the fact that eight of the twelve trainees supported by this program in the last reporting period obtained independent fellowships. The primary training facility IS TJL, a private, independent research center. TJL is an NCI-designated Cancer Center, with a research budget of $53.9 million, raises 3 million mice annually, and has held NIH research training grants continuously since 1956.